Electric storage device, electric storage apparatus, method for producing electric storage device, and method for producing cover plate

ABSTRACT

The electric storage device according to the present invention includes a case having a case body and a cover plate, the case body includes a step portion at an opening edge, the cover plate includes a projection that is inserted into the opening of the case body, and a portion of the projection opposes the step portion within the case body.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2013-31289, the disclosure of which is incorporated herein by referencein its entirety.

FIELD

The present invention relates to an electric storage device including:an electrode assembly; and a case including a case body that houses theelectrode assembly and a cover plate that covers an opening of the casebody, and to an electric storage apparatus including such an electricstorage device, a method for producing an electric storage device, and amethod for producing a cover plate.

BACKGROUND

In recent years, rechargeable electric storage devices such as batterycells (lithium ion battery cells, nickel hydrogen battery cells, etc.)and capacitors (electric double layer capacitors, etc.) are employed asa power source, for example, for vehicles (automobiles, motorcycles,etc.) and various equipment (mobile terminals, laptop computers, etc.).

For example, a battery cell (can-type battery cell) disclosed in PatentLiterature 1 includes: an electrode assembly (power generating element);and a case (housing case) having a case body (can) that houses theelectrode assembly and a cover plate (cover) that closes an opening ofthe case body. In a method for producing such a case body, anunnecessary portion such as a burr remains at an opening edge of theopening of the case body. This unnecessary portion is subjected tomachining such as trimming, so as to be cut off from the opening edge ofthe opening of the case body. Therefore, a step portion that is one steplower than other portions of the opening edge of the opening that havenot undergone machining may be formed in some cases at the opening edgeof the opening where the unnecessary portion has been present.

In such a case, this step portion forms a gap between the cover plateand the opening edge of the opening of the case body, when the coverplate is placed on the opening of the case body. Eventually, when a seambetween the cover plate and the opening edge of the opening of the casebody is laser welded, the laser beam penetrates through the gap into thecase. Thereby, the laser beam may possibly affect the contents such as aresin plate provided within the case.

The step portion formed at the opening edge of the opening of the casebody also includes a step portion formed in a portion of the opening foroptically detecting the orientation of the case, in addition to theabove-mentioned step portion. Such a step portion also has a possibilityof affecting the contents.

A battery cell (rectangular battery cell) disclosed in Patent Literature2 includes an electrode assembly (battery element), a case body (bodycase) that houses the electrode assembly, and a cover plate (cover) thatcloses an opening of the case body. The cover plate is provided with abase portion projecting toward the inside of the case body. This batterycase is sealed by fitting the base portion of the cover plate into theopening of the case body.

Therefore, when the seam between the cover plate and the opening edge ofthe opening of the case body is laser welded, even if the laser beam haspassed through this gap, the base portion of the cover plate blocks theway of the laser beam. Therefore, the laser beam does not penetrate intothe contents within the case.

However, the base portion of Patent Literature 2 planarly projectsuniformly from the cover plate toward the inside of the case body.Therefore, a capacity equivalent to the volume of the base portion isnot available as a capacity to house the electrode assembly within thecase. That is, the capacity equivalent to the volume of the base portionof the cover plate is lost from the capacity of the case. Since thecapacity equivalent to the volume of the base portion of the cover platedoes not contribute to the electricity storage by the battery cell, theelectric storage capacity per unit volume of the battery cell isreduced.

Such problems are not limited to batteries, and the same problems applyalso to capacitors (such as electric double layer capacitors).

CITATION LIST

-   Patent Literature 1: JP 2005-332700 A-   Patent Literature 2: JP 10 (1998)-269999 A

SUMMARY

The present invention aims to provide an electric storage device, anelectric storage apparatus, a method for producing an electric storagedevice, and a method for producing a cover plate, which are capable ofsuppressing a reduction in capacity inside the case and preventing, whena seam between an opening edge of an opening of a case body and a coverplate covering the opening is laser welded, the laser beam frompenetrating into contents within a case.

The following presents a simplified summary of the invention disclosedherein in order to provide a basic understanding of some aspects of theinvention. This summary is not an extensive overview of the invention.It is intended to neither identify key or critical elements of theinvention nor delineate the scope of the invention. Its sole purpose isto present some concepts of the invention in a simplified form as aprelude to the more detailed description that is presented later.

An the electric storage device according to an aspect of the presentinvention includes: an electrode assembly including a positive electrodeplate and a negative electrode plate that are insulated from each other;and a case that houses the electrode assembly, wherein the case includesa case body having an opening, and a cover plate that is placed on anopening edge of the opening of the case body so as to cover the opening,the case body includes a step portion at the opening edge, the coverplate includes a projection that is inserted into the opening of thecase body, a portion of the projection opposes the step portion withinthe case body, and a seam between the cover plate and the opening edgeof the case body is laser welded in at least the step portion.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other features of the present invention will becomeapparent from the following description and drawings of an illustrativeembodiment of the invention in which:

FIG. 1 is a perspective view of a battery cell according to anembodiment of the present invention;

FIG. 2 is a side view of the battery cell according to the embodiment;

FIG. 3 is a sectional view, taken along the line in FIG. 1, of thebattery cell according to the embodiment;

FIG. 4 is a bottom view of a cover plate of a case of the battery cellaccording to the embodiment;

FIG. 5 is an enlarged sectional view, taken along the line V-V in FIG.1, of the cover plate according to the embodiment;

FIG. 6 is an enlarged sectional view, taken along the line VI-VI in FIG.1, of the cover plate according to the embodiment;

FIG. 7 is an enlarged sectional view of the cover plate of the batterycell according to the embodiment when being placed on a case body;

FIG. 8 is an enlarged sectional view, for explaining the height of aprojecting ridge, of the cover plate according to the embodiment;

FIG. 9 is a bottom view of a cover plate according to another embodimentof the present invention;

FIG. 10 is a bottom view of a cover plate according to still anotherembodiment of the present invention;

FIG. 11 is a bottom view of a cover plate according to still anotherembodiment of the present invention;

FIG. 12 is a bottom view of a cover plate according to still anotherembodiment of the present invention;

FIG. 13 is a bottom view of a cover plate according to still anotherembodiment of the present invention;

FIG. 14 is an enlarged sectional view of a case body and a cover plateaccording to still another embodiment of the present invention;

FIG. 15 is an enlarged sectional view of a case body and a cover plateaccording to still another embodiment of the present invention;

FIG. 16 is an enlarged sectional view of a case body and a cover plateaccording to still another embodiment of the present invention;

FIG. 17 is a top view of a case body according to still anotherembodiment of the present invention;

FIG. 18 is a bottom view of a cover plate according to the embodiment;

FIG. 19 is a bottom view of a cover plate according to still anotherembodiment of the present invention;

FIG. 20 is a bottom view of a cover plate according to still anotherembodiment of the present invention; and

FIG. 21 is a perspective view of an electric storage apparatus includingthe electric storage device according to the present invention.

DESCRIPTION OF EMBODIMENTS

The electric storage device according to an aspect of this embodimentincludes: an electrode assembly including a positive electrode plate anda negative electrode plate that are insulated from each other; and acase that houses the electrode assembly, wherein the case includes acase body having an opening, and a cover plate that is placed on anopening edge of the opening of the case body so as to cover the opening,the case body includes a step portion at the opening edge, the coverplate includes a projection that is inserted into the opening of thecase body, at least a portion of the projection opposes the step portionwithin the case body, and a seam between the cover plate and the openingedge of the case body is laser welded in at least the step portion.

According to such a configuration, when the cover plate is placed on theopening edge of the opening of the case body, a gap is formed betweenthe cover plate and the opening edge due to the step portion provided atthe opening edge of the case body. However, the projection of the coverplate is arranged inside the gap as seen from the outside of the casebody. Therefore, when the seam between the cover plate and the openingedge of the opening of the case body is laser welded, even if the laserbeam has passed through this gap, the way of the laser beam is blockedby the projection of the cover plate, and it does not enter the insideof the case over the projection. Moreover, the projection is merelyprovided partially on the cover plate, and thus only a capacityequivalent to the volume of the projection is lost partially from thecapacity of the case. As a result, the capacity inside the case is notsignificantly reduced.

According to another aspect, the electric storage device of thisembodiment may have a configuration in which the cover plate includes arecess on an outer surface side of the portion where the projection isprovided.

When the projection is provided on the cover plate, the weight of thecover plate may well increase to the extent corresponding to the volumeof the projection. However, according to the above-mentionedconfiguration, since the recess is provided on the outer surface side ofthe portion where the projection is provided, the weight can be reducedto the extent corresponding to the capacity of the recess. Accordingly,the projection can block the laser beam so as to prevent the penetrationof the laser beam into the contents of the case, while the recesssuppresses the increase in weight of the cover plate.

According to another aspect, the electric storage device of thisembodiment may have a configuration in which the case body has abottomed rectangular tubular shape, the step portion extends over atleast one entire side of the opening edge of the case body, and theprojection is formed at a position corresponding to the at least oneside.

In this way, when the case body has a bottomed rectangular tubularshape, the step portion is formed over at least one entire side of thesides constituting the polygonal opening edge of the case body. At thistime, the gap is formed between the cover plate and the side of theopening edge. However, according to the above-mentioned configuration,the projection of the cover plate is arranged inside the gap as seenfrom the outside of the case body. Therefore, even if the laser beam haspassed through this gap in the laser welding, the way of the laser beamis blocked by the projection of the cover plate, and thus the laser beamdoes not enter the inside of the case over the projection. Moreover, theprojection is merely formed partially therein corresponding to the sideof the opening edge of the case body where the step portion is formed.Thus, only a capacity equivalent to the volume of the projection is lostpartially from the capacity of the case. As a result, the capacityinside the case is not significantly reduced.

In this case, the configuration may be such that the case body has abottomed quadrangular tubular shape, the step portion extends over eachof a pair of opposed entire sides of the opening edge of the case body,and the projection is formed on the cover plate at a positioncorresponding to at least the pair of sides.

When the case body has a bottomed quadrangular tubular shape as above,the step portion is formed extending over each of the pair of opposedentire sides of the sides that constitute the quadrangular opening edgeof the case body, and the gap is formed between the cover plate and atleast a pair of sides of the four sides that constitute the openingedge. However, the projection of the cover plate is arranged inside thegap as seen from the outside of the case body. Therefore, even if thelaser beam has passed through this gap in the laser welding, the way ofthe laser beam is blocked by the projection of the cover plate, and thusthe laser beam does not enter the inside of the case over theprojection. Moreover, the projection is merely formed partially thereincorresponding to each of the pair of sides of the opening edge of thecase body where the step portion is formed. Therefore, only a capacityequivalent to the volume of the projection is lost partially from thecapacity of the case. As a result, the capacity inside the case is notsignificantly reduced.

According to another aspect, the electric storage device of thisembodiment may have a configuration in which the projection has anannular shape that extends along the opening edge of the case body.

According to such a configuration, even if the step portion is formed atany position of the opening edge of the case body, the projection of thecover plate is arranged inside the gap formed between the cover plateand the opening edge. Therefore, even if the laser beam has passedthrough this gap in the laser welding, the way of the laser beam isblocked by the projection of the cover plate, and thus the laser beamdoes not enter the inside of the case over the projection. Moreover,since the projection is merely formed to have an annular shape thatextends along the inside of the opening edge of the case body, only acapacity equivalent to the volume of the projection is lost partiallyfrom the capacity of the case. As a result, the capacity inside the caseis not significantly reduced.

According to still another aspect, the electric storage device of thisembodiment may have a configuration in which the projection is incontact with or adjacent to an inner surface of the opening edge of thecase body.

According to such a configuration, the projection of the cover plateplaced on the opening edge of the opening of the case body abuts theinner surface of the opening edge of the case body, thereby allowing thecover plate to be positioned at a specific position.

According to another aspect, the electric storage device of thisembodiment may have a configuration in which the cover plate furtherincludes a case inner side portion that is inserted into the opening ofthe case body and is in contact with or adjacent to the inner surface ofthe opening edge, and the projection projects from the case inner sideportion.

According to such a configuration, the case inner side portion of thecover plate placed on the opening edge of the opening of the case bodyabuts the inner surface of the opening edge of the case body, therebyallowing the cover plate to be positioned at a specific position.Further, the projection having a height increased by the case inner sideportion is arranged inside the gap formed between the cover plate andthe opening edge. Therefore, even if the laser beam has passed throughthis gap in the laser welding, the way of the laser beam is blocked byeither the case inner side portion or the projection. This prevents thelaser beam from entering the inside of the case over the end of the caseinner side portion or the projection.

According to another aspect, the electric storage device of thisembodiment may have a configuration in which the projection is locallylocated in a vicinity of a circumference edge of the cover plate.

According to such a configuration, the projection is merely providedlocally in the circumference edge portion of the cover plate, and thusonly a capacity equivalent to the volume of the projection is lostpartially from the capacity of the case. As a result, the capacityinside the case is not significantly reduced.

According to another aspect, the electric storage device of thisembodiment may have a configuration in which the projection has an outercircumferential edge spaced at a distance from the inner surface of theopening edge.

According to another aspect, the electric storage device of thisembodiment may have a configuration in which the projection has a linearshape that extends along the opening edge of the case body.

According to such a configuration, since the projection merely has aprojecting shape that extends along the opening edge of the case body,only a capacity equivalent to the volume of the projection is lostpartially from the capacity of the case. As a result, the capacityinside the case is not significantly reduced.

According to another aspect, the electric storage device of thisembodiment may have a configuration in which the projection has a tip inthe projecting direction with an arcuate cross section.

According to such a configuration, it is possible to suppress thegeneration of metal powder, etc., due to the abrasion between theprojecting ridge and the inner side of the case body when the coverplate is fitted into the case body.

An electric storage apparatus according to this embodiment includes: atleast two electric storage devices including at least one electricstorage device according to any one of the above-described aspects; anda coupling member that couples the at least two electric storage devicesto each other.

A method for producing an electric storage device according to thisembodiment, in which the electric storage device includes: an electrodeassembly including a positive electrode plate and a negative electrodeplate that are insulated from each other; and a case that houses theelectrode assembly and includes a case body having an opening, and acover plate configured to cover the opening of the case body, includes:a step of irradiating a seam between the cover plate and an opening edgeof the opening of the case body with a laser, with the cover plate beingplaced on the opening edge of the opening of the case body, wherein thecase body includes a step portion at the opening edge, the cover plateincludes a projection that is inserted into the opening of the casebody, at least a portion of the projection opposes the step portionwithin the case body, and the seam is irradiated with the laser at aposition corresponding to the step portion in the laser irradiationstep.

According to such a configuration, when the cover plate is placed on theopening edge of the opening of the case body, a gap is formed betweenthe cover plate and the opening edge due to the step portion provided atthe opening edge of the case body. However, the projection of the coverplate is arranged inside the gap as seen from the outside of the casebody. Therefore, when the seam between the cover plate and the openingedge of the opening of the case body is laser welded, even if the laserbeam has passed through this gap, the way of the laser beam is blockedby the projection of the cover plate, and it does not enter the insideof the case over the projection.

According to one aspect, the method for producing an electric storagedevice of this embodiment may have a configuration in which theprojection is formed by coining the cover plate from its outer surfacetoward its inner surface.

Such a configuration can suppress an increase in weight of the coverplate by providing the projection.

According to another aspect, the method for producing an electricstorage device of this embodiment may have a configuration in which acircumference edge portion of the cover plate, which is placed on theopening edge of the case body, is subjected to compression molding.

According to such a configuration, the circumference edge portion of thecover plate is subjected to compression molding, so as to have athickness smaller than the other portions. Therefore, when thecircumference edge portion of the cover plate is placed on the openingedge of the opening of the case body, the portions other than thecircumference edge portion of the cover plate relatively enter theinside of the case body. Thus, the height of the projection is increasedto the extent that the cover plate has entered the inside of the casebody. As a result, even if the laser beam has passed through this gap inthe laser welding, the way of the laser beam is more reliably blocked bythe projection of the cover plate having an increased height.

According to another aspect, the method for producing an electricstorage device of this embodiment may have a configuration in which theprojection is locally located in a vicinity of a circumference edge ofthe cover plate.

According to such a configuration, the projection is merely providedlocally in the circumference edge portion of the cover plate, and thusonly a capacity equivalent to the volume of the projection is lostpartially from the capacity of the case. As a result, the capacityinside the case is not significantly reduced.

According to another aspect, the method for producing an electricstorage device of this embodiment may have a configuration in which theprojection has an outer circumferential edge spaced at a distance fromthe inner surface of the opening edge.

According to another aspect, the method for producing an electricstorage device of this embodiment may have a configuration in which theprojection has a linear shape that extends along the opening edge of thecase body.

According to such a configuration, since the projection merely has aprojecting shape that extends along the opening edge of the case body,only a capacity equivalent to the volume of the projection is lostpartially from the capacity of the case. As a result, the capacityinside the case is not significantly reduced.

According to another aspect, the method for producing an electricstorage device of this embodiment may have a configuration in which theprojection has a tip in the projecting direction with an arcuate crosssection.

According to such a configuration, it is possible to suppress thegeneration of metal powder, etc., due to the abrasion between theprojecting ridge and the inside of the case body when the cover plate isfitted into the case body.

According to another aspect, the method for producing an electricstorage device of this embodiment may have a configuration in which thecover plate includes a case inner side portion that is inserted into theopening of the case body, and a thin portion that is formed around acircumference edge of the cover plate and has a thickness smaller thanthe case inner side portion, the projection projects from the case innerside portion, and H2≧H1+H3−H0 is satisfied, when a dimension in thethickness direction of the case inner side portion is H0, a dimension inthe thickness direction of the thin portion is H1, a dimension in thethickness direction of the projection is H2, and a height difference inthe thickness direction of the step portion is H3.

According to such a configuration, the inner side portion or theprojection of the cover plate is reliably arranged inside the gapbetween the cover plate and the opening edge of the case body as seenfrom the outside of the case body.

A method for producing a cover plate according to this embodiment is amethod for producing a cover plate configured to cover an opening of acase body that houses an electrode assembly including a positiveelectrode plate and a negative electrode plate that are insulated fromeach other, and the method includes forming a projection that opposes,within the case body, a step portion formed at an opening edge of theopening of the case body, with the cover plate being placed on theopening edge, by coining the cover plate at a corresponding positionfrom its outer surface toward its inner surface.

According to such a configuration, when the cover plate is placed on theopening edge of the opening of the case body, a gap is formed betweenthe cover plate and the opening edge due to the step portion provided atthe opening edge of the case body. However, the projection of the coverplate is arranged inside the gap as seen from the outside of the casebody. Therefore, when the seam between the cover plate and the openingedge of the opening of the case body is laser welded, even if the laserbeam has passed through this gap, the way of the laser beam is blockedby the projection of the cover plate. This prevents the laser beam fromentering the inside of the case over the projection. Moreover, theprojection is formed by coining the cover plate, and therefore theweight of the cover plate does not increase due to providing theprojection. Therefore, the capacity inside the case is not reduced.

According to one aspect, the method for producing a cover plate of thisembodiment may have a configuration in which a circumference edgeportion of the cover plate, which is placed on the opening edge of thecase body, is subjected to compression molding.

According to such a configuration, the circumference edge portion of thecover plate is subjected to compression molding, thereby allowing theportions other than the circumference edge portion of the cover plate torelatively enter the inside of the case body. Thus, the height of theprojection is increased to the extent that the cover plate has enteredthe inside of the case body. As a result, even if the laser beam haspassed through this gap in the laser welding, the way of the laser beamis blocked by the projection of the cover plate having an increasedheight, so that the laser beam does not enter the inside of the case.

As has been described above, according to this embodiment, it ispossible to prevent the laser beam from penetrating into the contentsinside the case, when the seam between the cover plate and the openingedge of the opening of the case body is laser welded, without reducingthe electric storage capacity.

Hereinafter, a battery cell as an embodiment of the electric storagedevice according to the present invention is described with reference tothe drawings. The battery cell according to this embodiment is anon-aqueous electrolyte secondary battery cell, more specifically, alithium ion secondary battery cell. As shown in FIG. 1 to FIG. 8, thebattery cell according to this embodiment includes a case 1 composed ofa case body 2 having an opening, and a cover plate 3 that is placed onan opening edge of the opening of the case body 2 so as to close andseal the opening. Further, the battery cell includes an electrodeassembly 4 housed within the case 1 and a terminal structure 9 that isprovided on the cover plate 3 so as to be electrically connected withthe electrode assembly 4.

The case body 2 and the cover plate 3 of the case 1, for example, aremade of aluminum or an aluminum-based metal material such as aluminumalloy. As shown in FIG. 1 to FIG. 3, the case body 2 has a bottomedrectangular tubular shape that is flattened in the width direction so asto house the electrode assembly 4 of a wound type with an elongatedcylindrical shape. The cover plate 3 is a plate member having arectangular shape corresponding to the shape of the opening of the casebody 2.

The case body 2 has a pair of opposed side plates 2 b and a pair ofopposed end plates 2 c that are erected from the circumference edge of arectangular bottom 2 a in the first direction A1 (height direction). Thepair of end plates 2 c are erected from the edge of the bottom 2 a thatextends along a second direction A2 that is the short direction of therectangular bottom 2 a. Further, the pair of side plates 2 b are erectedfrom the edge of the bottom 2 a that extends along a third direction A3that is the longitudinal direction of the bottom 2 a. The case body 2 isformed to have a thin bottomed quadrangular tubular shape with a smalldepth by having the pair of end plates 2 c with a smaller width (thanthe pair of side plates 2 b).

The pair of side plates 2 b each have a first side P1 provided on thebottom 2 a side, a second side P2 opposing the first side P1, and a pairof sides P3 and P4 extending along the first direction A1. Likewise, thepair of end plates 2 c each have a first side P1 provided on the bottom2 a side, a second side P2 opposing the first side P1, and a pair ofsides P3 and P4 extending along the first direction A1. An opening 2 dcorresponding to the bottom 2 a is formed in the region surrounded bythe second sides P2 of the pair of side plates 2 b and the second sidesP2 of the pair of end plates 2 c.

Meanwhile, in the production process of the case body 2, an unnecessaryportion such as a burr remains at the opening edge of the opening 2 d.In order to remove such an unnecessary portion at the opening edge ofthe opening 2 d, the region corresponding to the second sides P2 of thepair of side plates 2 b of the case body 2 and the region correspondingto the second sides P2 of the pair of end plates 2 c of the case body 2(specifically, the opening edge) are subjected to trimming. Thisgenerates a height difference in the region corresponding to the secondsides P2 of the pair of side plates 2 b of the case body 2 and theregion corresponding to the second sides P2 of the pair of end plates 2c of the case body 2. Thereby, a step portion S as shown in FIG. 8 isformed at the opening edge of the case body 2 (hereinafter, this stepportion S is referred to as “trimming step portion S”).

The trimming step portion S of this embodiment is formed by trimmingeach of the pairs of opposite sides of the opening edge of the case body2. The trimming step portion S is formed as follows, so that the regionsprovided at the opening edge of the case body 2 are reduced as much aspossible. The second sides P2 of the pair of end plates 2 c with asmaller width are trimmed to be lower than the second sides P2 of thepair of side plates 2 b. Thus, the trimming step portion S is formed ateach of the second sides P2 of the pair of end plates 2 c. At this time,the position at which the trimming step portion S is formed isdetermined depending on the processing method and the processingaccuracy for forming the opening edge of the case body 2, the acceptableamount of the unnecessary portion such as a burr, etc. For example, sucha case body 2 having a rectangular opening edge as in this embodiment isproduced by forming a bottomed rectangular tubular member by deepdrawing, and thereafter cutting the portion where the opening edge isintended to be provided. At this time, if the portion, where the openingedge is intended to be provided, of the bottomed rectangular tubularmember is cut along the long sides of the rectangular opening edge(specifically, the portion where the long sides of the opening edge areformed by cutting) in parallel thereto, the cutting starts at one shortside portion and ends at the other short side portion. In such aproduction process, a portion such as a burr remains in the pair ofshort side portions, which therefore are subjected to trimming, so thatthe trimming step portion S is formed along the pair of short sideportions. However, the remaining amount of the portion such as a burr issmaller at the position where the cutting starts than at the positionwhere the cutting ends. Therefore, the trimming step portion S may beformed only at the position where the cutting ends. Other than that, thetrimming step portion S may be locally formed at the second sides P2 ofthe pair of end plates 2 c, or may be formed along the entire secondsides P2 of the pair of end plates 2 c.

As shown in FIG. 4, the cover plate 3 has a rectangular shape. Twothrough holes 31 are formed in the cover plate 3 at intervals in thethird direction A3. Further, as shown in FIG. 1 to FIG. 4, a circulargas discharge valve 32 is formed integrally with the cover plate 3 atthe center of the cover plate 3. A thin portion having a substantiallyY-shape is formed in the gas discharge valve 32. The gas discharge valve32 reduces the pressure in the case 1 by splitting the thin portion inthe case where the internal pressure of the case 1 unusually increases.An injection hole 33 with a small diameter is formed in the cover plate3 on a lateral side of the gas discharge valve 32. This injection hole33 is closed by a stopper 13 after an electrolyte liquid is injectedinto the case 1.

The cover plate 3 includes a projection. This projection opposes, withinthe case 1, the trimming step portion S formed at the opening edge ofthe case body 2. In this embodiment, as shown in FIG. 5 and FIG. 6, aprojecting ridge 34 projecting linearly from the cover plate 3 isdescribed as an example of such a projection. The projecting ridge 34(projection) is locally located in the vicinity of the circumferenceedge of the cover plate 3 on the lower surface of the cover plate 3.This projecting ridge 34 is formed on the cover plate 3 at each of thepositions that conform to the second sides P2 of at least the pair ofend plates 2 c, corresponding to that the trimming step portion S isprovided at each of the second sides P2 of the pair of end plates 2 c.The projecting ridge 34 is provided on the cover plate 3 so as to be incontact with the inner surface of the opening edge of the case body 2.More specifically, the projecting ridge 34 is provided along each of thesecond sides P2 of the end plates 2 c on the cover plate 3 inside theregions of the circumference edge portion that abut the opening edge ofthe case body 2. Both ends of the projecting ridge 34 reach portions ofthe second sides P2 of the pair of side plates 2 b. The projecting ridge34 projects from the cover plate 3 along the pair of end plates 2 c ofthe case body 2. The projecting ridge 34 is formed by coining. That is,the projecting ridge 34 is a portion formed by depressing the coverplate 3 on the upper surface (outer surface) side of the cover plate 3into a recess, and raising the cover plate 3 on the lower surface (innersurface) side thereof into a projection. A recess 35 is formed on theupper surface (outer surface) of the cover plate 3 at a positioncorresponding to the position where the projecting ridge 34 is formed onthe lower surface (inside) of the cover plate 3. The capacity of therecess 35 depressed on the upper surface of the cover plate 3 issubstantially the same as the volume of the projecting ridge 34 raisedon the lower surface of the cover plate 3. The projecting ridge 34 has atip portion in the projecting direction with an arcuate cross section.This can suppress the generation of metal powder, etc., due to theabrasion between the projecting ridge 34 and the inner side of the casebody 2 when the cover plate 3 is fitted into the case body 2.

As shown in FIG. 7, the cover plate 3 has a thin portion 36 formed bycompression molding of the lower surface side of the circumference edgeportion in the thickness direction. The thin portion 36 is a portionhaving a reduced thickness as compared to portions of the cover plate 3other than the thin portion 36. The thin portion 36 is formed by raisingthe lower surface side of the circumference edge portion one step higherin the thickness direction of the cover plate 3. Providing of the thinportion 36 allows a case inner side portion 37 that comes into contactwith the inner surface of the opening edge of the case body 2 by beinginserted into the opening 2 d of the case body 2 to be formed in thecover plate 3. The thin portion 36 is provided at a portion opposing theopening edge of the opening 2 d of the case body 2 over the entirecircumference of the cover plate 3.

Here, the height in the thickness direction of the projecting ridge 34from the upper surface of the cover plate 3 (dimension in the thicknessdirection) is described with reference to FIG. 8. When the height in thethickness direction of the case inner side portion 37 (the height fromthe upper surface of the cover plate 3) is H0, the height H1 of the thinportion 36 of the cover plate 3 is lower than the height H0 of the caseinner side portion 37 (H1<H0). The projecting ridge 34 projects from thelower end of the case inner side portion 37 where the thin portion 36 ofthe cover plate 3 is not provided. Therefore, when the height in thethickness direction of the projecting ridge 34 itself is H2, the heightof the projecting ridge 34 from the upper surface of the cover plate 3is a value (=H0+H2) obtained by adding the height H2 of the projectingridge 34 itself to the height H0 of the case inner side portion 37.

On the other hand, when the height difference of the trimming stepportion S itself is H3, the height, from the upper surface of the coverplate 3, at the lower end of a gap G formed between the cover plate 3and the opening edge of the opening 2 d of the case body 2 due toforming the trimming step portion S is a value (=H1+H3) obtained byadding the height difference H3 of the trimming step portion S itself tothe height H1 of the thin portion 36 of the cover plate 3. The height H2of the projecting ridge 34 itself (H2≧H1+H3−H0) is set so that theheight of the projecting ridge 34 from the upper surface of the coverplate 3 exceeds the height at the lower end of the gap G from the uppersurface of the cover plate 3. Therefore, the height H2 of the projectingridge 34 itself on the circumference edge side of the cover plate 3(that is, the height difference between the lower surface of the thinportion 36 and the lower end of the projecting ridge 34) is increased byproviding the thin portion 36 in the circumference edge portion of thecover plate 3 to the extent that the thickness of the thin portion 36 isreduced from the height H0 of the case inner side portion 37 (H0−H1), ascompared to the case where the thin portion 36 is not provided in thecircumference edge portion of the cover plate 3. In other words, it ispossible to close the gap G formed between the cover plate 3 and theopening edge of the opening 2 d of the case body 2 without changing theheight of the projecting ridge 34 (the height of the projecting ridge 34from the upper surface of the cover plate 3), even if the heightdifference H3 of the trimming step portion S is increased to the extentthat the thickness of the thin portion 36 is reduced from the height H0of the case inner side portion 37. It should be noted that the trimmingstep portion S according to this embodiment is formed at an angle so asto slope downwardly from the inner circumferential surface side to theouter circumferential surface at the opening edge of the case body 2. Inother words, the height difference H3 of the trimming step portion S isincreased from the inner circumferential surface toward the outercircumferential surface of the opening edge. In the above-mentionedrelationship of the height of the projecting ridge 34, the heightdifference H3 of the trimming step portion S itself is preferablydefined by the height difference on the inner circumferential surfaceside of the opening edge.

As shown in FIG. 3, the electrode assembly 4 is formed by winding astrip-shaped positive electrode sheet 5 and a strip-shaped negativeelectrode sheet 6 with a strip-shaped separator 7 interposedtherebetween into an elongated cylindrical shape that forms a circleelongated in the up-down direction about the rotation axis in theleft-right direction. At this time, the positive electrode sheet 5 andthe negative electrode sheet 6 are shifted from each other in thedifferent directions to the left and right sides. The electrode assembly4 is housed within the case 1 while being entirely covered by aninsulating cover made of an insulating sheet so as to be insulated fromthe case 1. The positive electrode sheet 5 is formed of an aluminum foilon the surface of which a positive electrode active material issupported. The negative electrode sheet 6 is formed of a copper foil onthe surface of which a negative electrode active material is supported.The positive electrode sheet 5 and the negative electrode sheet 6 haveportions that are not coated with the active materials respectively attheir end edges in the shift direction on the left and right sides. Inthis way, the aluminum foil and the copper foil are exposed at the leftand right ends of the electrode assembly 4. That is, at the left andright ends of the electrode assembly 4, metal foils of the electrodes(portions of the electrodes to which no active materials are applied)are wound into a rolled bundle.

Further, a current collector 8 is electrically connected to each of themetal foils exposed at the left and right ends of the electrode assembly4. The current collector 8 is an electrically conductive metal memberelongated in the up-down direction. More specifically, the currentcollector 8 for the positive electrode, for example, is formed usingaluminum or aluminum alloy. The current collector 8 for the negativeelectrode, for example, is formed using copper or copper alloy. An upperpart of the current collector 8 is folded horizontally, as shown in FIG.7, to serve as a connecting portion 8 a. A portion of the currentcollector 8 that is lower than the connecting portion 8 a is dividedinto two on the front and rear sides, which project downwardly. Theportion divided into two is gripped by clip plates together with the endof the electrode assembly 4 so as to be connected and fixed to the endof the electrode assembly 4, for example, by ultrasonic welding.

As shown in FIG. 3 and FIG. 7, the terminal structure 9 includes theterminal structure 9 for the positive electrode and the terminalstructure 9 for the negative electrode. Each terminal structure 9includes a resin plate 10, an outer gasket (gasket) 11, and an externalterminal 12. The resin plate 10 and the outer gasket 11 are arranged oneach of the left and right sides of the cover plate 3 so as to surroundthe through holes 31 from the inner and outer sides. The externalterminal 12 is inserted through the corresponding through hole 31 viathe resin plate 10 and the outer gasket 11, and is electricallyconnected to the connecting portion 8 a of the current collector 8. Thisallows the electrode assembly 4 within the case 1 and the externalterminal 12 to be electrically connected to each other.

The external terminal 12 includes the external terminal 12 for thenegative electrode and the external terminal 12 for the positiveelectrode. Each external terminal 12 has a head 12 a and a stem 12 bextending downwardly from the center on the lower surface of the head 12a. A bus bar is connected to the surface (exposed surface) of the head12 a by welding. The external terminal 12 for the negative electrode,for example, is formed using copper or copper alloy. The externalterminal 12 for the positive electrode, for example, is formed usingaluminum or aluminum alloy.

In production of a battery cell 1 with the above-described structure,the electrode assembly 4 in which the positive electrode sheet 5, thenegative electrode sheet 6, the separator 7, and the current collector 8are assembled is first housed within the case body 2 through the opening2 d of the case body 2. Subsequently, the cover plate 3 is placed on theopening edge of the opening 2 d of the case body 2 at an appropriateposition. At this time, the cover plate 3 is positioned by theprojecting ridge 34 with respect to the opening 2 d of the case body 2.The cover plate 3 is coupled to the case body 2 by laser welding overthe entire circumference of the seam with the opening 2 d of the casebody 2. This allows the opening 2 d of the case body 2 to be closed bythe cover plate 3 so that the case 1 is sealed. After the case 1 is thussealed, the outer gasket 11 is placed on the cover plate 3, and theexternal terminal 12 is inserted through an opening of the outer gasket11, the through hole 31 of the cover plate 3, and an opening of theconnecting portion 8 a of the current collector 8 arranged within thecase 1. Then, an external force is applied from the outside of the case1 so that the tip portion of the external terminal 12 is crimped,thereby allowing the external terminal 12 and the electrode assembly 4to be electrically connected to each other. As a result, the batterycell 1 is accomplished.

As described above, according to the battery cell 1 of this embodiment,when the cover plate 3 is placed on the opening edge of the opening 2 dof the case body 2, the gap G is formed between the cover plate 3 andthe opening edge due to the trimming step portion S provided at theopening edge of the case body 2. However, the projecting ridge 34 of thecover plate 3 is arranged inside the gap G as seen from the outside ofthe case body 2. Therefore, even if a laser beam L enters this gap Gwhen the seam between the opening edge of the opening 2 d of the casebody 2 and the cover plate 3 is laser welded, the way of the laser beamL is blocked by the projecting ridge 34 of the cover plate 3. Thus, thelaser beam L does not penetrate into the case 1. Moreover, theprojecting ridge 34 is merely provided partially in the cover plate 3 soas to correspond to the entire length of each of the second sides P2 ofthe pair of end plates 2 c in which the trimming step portion S isformed. Therefore, only a capacity equivalent to the volume of theprojecting ridge 34 is lost partially from the capacity of the case 1,so that the capacity inside the case 1 is not significantly reduced.

Further, when the projecting ridge 34 is provided in the cover plate 3,the weight of the cover plate 3 may well increase to the extentcorresponding to the volume of the projecting ridge 34. However, sincethe recess 35 is provided on the outer surface side of the portion wherethe projecting ridge 34 is provided, the weight of the cover plate 3 canbe reduced to the extent corresponding to the capacity of the recess 35.Accordingly, the laser beam L is blocked by the projecting ridge 34 sothat the laser beam L does not penetrate into the case 1, while theincrease in weight of the cover plate 3 is suppressed by the recess 35.Particularly, according to a method for producing the cover plate 3 ofthis embodiment, the projecting ridge 34 is formed by coining the coverplate 3, and therefore the weight of the cover plate 3 does not increaseby providing the projecting ridge 34. Therefore, the electric storagecapacity per unit weight of the battery cell 1 is also not reduced.

Further, when the cover plate 3 is placed on the opening edge of theopening 2 d of the case body 2, the case inner side portion 37 of thecover plate 3 abuts the inner surface of the opening edge of the casebody 2, thereby allowing the cover plate 3 to be positioned at aspecific position. Further, since the circumference edge portion of thecover plate 3 is subjected to compression molding, the case inner sideportion 37 of the cover plate 3 relatively enters the inside of the casebody 2. The height of the projecting ridge 34 is increased to the extentthat the cover plate 3 has entered the inside of the case body 2.Therefore, even if the laser beam L is about to penetrate through thegap G between the cover plate 3 and the opening edge of the case body 2in the laser welding, the way of the laser beam L is blocked by theprojecting ridge 34 of the cover plate 3 having an increased height.Thus, the laser beam L does not penetrate into the case 1.

It should be noted that the electric storage device according to thepresent invention is not limited to the above-mentioned embodiments, andvarious modifications can be made without departing from the gist of theinvention.

For example, the above-mentioned embodiments describe an example inwhich the projecting ridge 34 is formed to be unevenly distributed inthe cover plate 3 (that is, so as to be locally located in the vicinityof the circumference edge of the cover plate 3) corresponding to thesecond sides P2 of the pair of end plates 2 c and partially to the endportions of the second sides P2 of the pair of side plates 2 b. However,the projecting ridge 34 may be provided at any position as long as theposition opposes the trimming step portion S within the case 1. Forexample, as shown in FIG. 9, projections 134 may be formed correspondingrespectively to the second sides P2 of the pair of side plates 2 b. Thepair of projections 134 are formed along the entire length of the secondsides P2 of the pair of side plates 2 b, and both ends of the pair ofprojections 134 reach the connecting portions between the side plates 2b and the end plates 2 c. That is, both ends of the projections 134 arebent (curved) inwardly, and the projections 134 between the ends extendlinearly. When a step portion is provided on each of the second sides P2of the pair of side plates 2 b of the opening edge of the case body 2,penetration of the laser beam can be prevented. Further, theconfiguration of a cover plate 103 provided with the pair of projections134 enables the cover plate 103 to be positioned in the second directionA2 with respect to the opening 2 d of the case body 2, in addition tothe prevention of the laser penetration.

Further, as shown in FIG. 10, a projection 234 may be formed to have anannular shape that extends along the inside of the opening edge of thecase body 2. Even if the step portion is formed at any position of theopening edge of the case body 2, the projection 234 of a cover plate 203is arranged inside the gap formed between the cover plate 203 and theopening edge. In the laser welding, even if the laser beam is about topenetrate through the gap formed between the cover plate 203 and theopening edge, the way of the laser beam is blocked by the projection 234of the cover plate 203. Thus, the laser beam does not penetrate into thecase 1. Further, since the projection 234 is merely formed to have anannular shape that extends along the inside of the opening edge of thecase body 2, only a capacity equivalent to the volume of the projection234 is lost partially from the capacity of the case 1. Therefore, thecapacity inside the case 1 is not significantly reduced. Further, theconfiguration of the cover plate 203 provided with the projection 234having an annular shape enables the cover plate 203 to be positioned inboth the second direction A2 and the third direction A3 with respect tothe opening 2 d of the case body 2, in addition to the prevention of thelaser penetration.

Further, as shown in FIG. 11, a projection 334 may be formedcorresponding to each of the connecting portions (the corner portions ofthe case body 2) of the opening edge of the case body 2 between the sideplates 2 b and the end plates 2 c. The projection 334 may be formedcorresponding to each of the connecting portions (four corners) betweenthe side plates 2 b and the end plates 2 c in the case body 2, or may beformed corresponding to some of the connecting portions between the sideplates 2 b and the end plates 2 c. In such a case, when the corners ofthe case body 2 are trimmed, and a step portion is formed at theconnecting portions between the side plates 2 b and the end plates 2 cof the opening edge of the case body 2, the laser penetration can beprevented. Further, the configuration in which the projection 334 isprovided corresponding to each of the (four) connecting portions of thecase body 2 enables a cover plate 303 to be positioned in both thesecond direction A2 and the third direction A3 with respect to theopening 2 d of the case body 2, in addition to the prevention of thelaser penetration.

The above-mentioned embodiments describe an example in which theprojection 34 is formed corresponding to each of a pair of the opposedsides of the sides that constitute the substantially rectangular openingedge of the case body 2. However, as shown in FIG. 12, a projection 434may be formed corresponding to at least one of the sides that constitutethe substantially rectangular opening edge of the case body 2. Moreover,this projection 434 may be locally formed corresponding to a portion ofthe one side. For example, in the case where the step portion is formedof a notch or a recess that is provided at the opening 2 d of the casebody 2 for optically detecting the orientation of the case 1, the way ofthe laser beam is blocked in the laser welding by the projection 434when the projection 434 is provided corresponding to the position wherethe step portion is formed.

Further, as shown in FIG. 13, a pair of projections 534 may beconfigured as follows. Both ends of the projections 534 are in abuttingor adjacent contact with the side plates 2 b at the opening 2 d of thecase body 2, and the center portions of the projections 534 are inabutting or adjacent contact with the end plates 2 c. On the other hand,the portions between both ends and the center portions of theprojections 534 are not in abutting or adjacent contact with theconnecting portions between the side plates 2 b and the end plates 2 cof the case body 2. When a step portion is provided at the second sidesP2 of the pair of end plates 2 c of the opening edge of the case body 2,penetration of the laser beam can be prevented. Further, theconfiguration of a cover plate 503 provided with a pair of theprojections 534 enables the cover plate 503 to be positioned in both thesecond direction A2 and the third direction A3 with respect to theopening 2 d of the case body 2, in addition to the prevention of thelaser penetration.

Further, the above-mentioned embodiments describe an example in whichthe projecting ridge 34 (projection) is in contact with the innersurface of the opening edge of the case body 2. However, as shown inFIG. 14, a projection 634 may be adjacent to the inner surface of theopening edge of the case body 2. Also in this case, the projection 634blocks, when the seam between a cover plate 603 and the opening edge ofthe case body 2 is irradiated with the laser beam L in parallel, the wayof the laser beam L that has penetrated through the gap G formed betweenthe cover plate 603 and the opening edge into the case 1. This canprevent the laser beam L from further entering the inside of the case 1over the position where the projection 634 is provided.

Further, the above-mentioned embodiments describe an example in whichthe thin portion 36 is provided in the circumference edge portion of thecover plate 3. However, as shown in FIG. 15, the cover plate 3 does notneed to be provided with the thin portion 36. In this case, only aprojection 734 closes the gap G formed between a cover plate 703 and theopening edge due to the step portion, and the projection 734 blocks theway of the laser beam L penetrating through the gap G formed between thecover plate 703 and the opening edge. Thus, the laser beam L does notpenetrate into the case 1. Further, as shown in FIG. 16, a projection834 may be adjacent to the inner surface of the opening edge of the casebody 2. Also in this case, the projection 834 blocks the way of thelaser beam L, when the laser beam L with which the seam between theopening edge of the case body 2 and a cover plate 803 is irradiated inparallel has penetrated thereinto through the gap G formed between thecover plate 803 and the opening edge. This can prevent the laser beam Lfrom further entering the inside of the case 1 over the position wherethe projection 834 is provided.

Further, the above-mentioned embodiments describe an example in whichthe pair of projecting ridges 34 are provided respectively on both endsides of the cover plate 3. However, as shown in FIG. 14 to FIG. 16, aprojection 634, 734, 834 may be provided only on one end side of a coverplate 603, 703, 803. When a step portion is provided on one side of theopening edge of the case body 2, penetration of the laser can beprevented.

The above-mentioned embodiments describe an example in which the casebody 2 has a bottomed quadrangular tubular shape, and the cover plate 3is a rectangular plate member. That is, an example in which the case 1has a quadrangular box shape is indicated. However, as shown in FIG. 17,the present invention can be applied to a case body 902 having a shapesuch that an opening edge 902 d has a plurality of corner portions 902e, and a plurality of sides 902 b and 902 c that connect adjacent cornerportions 902 e. The plurality of sides 902 b correspond to the sideplates 2 b in the above-mentioned embodiments. The plurality of sides902 c correspond to the end plates 2 c in the above-mentionedembodiments. In the case of the case body 902 having the opening edgewith a shape that includes the corner portions 902 e, a pair ofprojections 934 are each provided in a cover plate 903 so as to be incontact with or adjacent to two adjacent corner portions 902 e and theside 902 c between the corner portions 902 e, as shown in FIG. 18. Thepair of projections 934 are each formed along the two adjacent cornerportions 902 e and the side 902 c between the corner portions 902 e.That is, the projections 934 are each formed into a so-called C shape.When the cover plate 903 is placed on the opening edge of the opening902 d of the case body 902, the plurality of projections 934 formed onthe cover plate 903 as above are in contact with or adjacent to theplurality of corner portions 902 e of the opening edge of the case body902. Also in this case, when the step portion is formed at the pluralityof corner portions 902 e, the projections 934 block the laser beam thatis about to penetrate through the gap formed between the cover plate 903and the opening edge or the way of the laser beam that has penetratedtherethrough, or prevent the laser beam from entering the inside of thecase 1 or prevent it from further entering thereinside. The projections934 are merely formed at the plurality of corner portions 902 e of theopening 902 d of the case body 902. Therefore, only a capacityequivalent to the volume of the projections 934 is lost partially fromthe capacity of the case, and the capacity inside the case 1 is notsignificantly reduced. Further, the configuration of the cover plate 903provided with the pair of projections 934 enables the cover plate 903 tobe positioned in both the second direction A2 and the third direction A3with respect to the opening 902 d of the case body 902, in addition tothe prevention of the laser penetration.

The pair of projections 934 may be provided in the cover plate 903 so asto be in contact with or adjacent to at least one of the plurality ofcorner portions 902 e. Also in this case, when the step portion isformed at the plurality of corner portions 902 e, the projections 934block the way of the laser beam that is about to penetrate, or that haspenetrated, through the gap formed between the cover plate 903 and theopening edge, or prevents the laser beam from entering the inside of thecase 1 or prevent it from further entering thereinside.

The present invention can be applied to a case in which a case body hasa bottomed cylindrical shape, and a cover plate 1003, 1103 is a circularplate member that closes the opening of the case body, as shown in FIG.19 and FIG. 20. In this case, as shown in FIG. 19, a projection 1034having an annular shape may be provided on the cover plate 1003 so as tooppose the entire inner circumference of the case body. Further, asshown in FIG. 20, a projection 1134 having an arcuate shape may beprovided on the cover plate 1103 so as to oppose portions of the insideof the case body. Also in these embodiments, when the projection 1034,1134 is provided at a position corresponding to the step portion formedat the opening edge of the opening 2 d of the case body 2, it ispossible to suppress the penetration of the laser beam into the casebody in laser welding.

Further, the above-mentioned embodiments describe an example in whichthe current collector 8 for the positive electrode and the externalterminal 12 for the positive electrode are formed using aluminum oraluminum alloy, and the current collector 8 for the negative electrodeand the external terminal 12 for the negative electrode are formed usingcopper or copper alloy. However, the materials for the currentcollectors 8 and the external terminals 12 are arbitrarily selected aslong as being an electrically conductive metal material corresponding tothe type of the battery cell. Further, the above-mentioned embodimentsalso exemplify the materials for the external terminals 12. However, thematerials for the external terminals 12 are arbitrarily selected as longas being an electrically conductive metal material that has suitableproperties such as strength and conductivity.

Further, the electrode assembly 4 is not limited to those of a woundtype with an elongated cylindrical shape, as in the above-mentionedembodiments, and may have another shape. The electrode assembly, forexample, may be of a stack type in which a plurality of positiveelectrode sheets and a plurality of negative electrode sheets arealternately stacked via separators.

Further, the above-mentioned embodiments describe an example in whichthe case 1 is formed using aluminum alloy, steel, or the like. However,the material for the case 1 (the case body 2 and the cover plate 3) isarbitrarily selected as long as being a metal material. Further, theshape and the structure of the case 1 (the case body 2 and the coverplate 3) are also not limited to the above-mentioned embodiments, andare arbitrarily selected.

Further, the above-mentioned embodiments describe an example in whichthe trimming step portion S is formed in the case body 2. However, thestep portion may be composed of a notch or a recess that is formedintentionally in part of the opening in order to optically detect theorientation of the case in some cases. Further, the step portion may beformed unintentionally due to errors in dimensional accuracy whenproducing the components or slight bumps. The present invention isapplicable also to these cases.

Further, the above-mentioned embodiments describe an example in whichthe thin portion 36 is produced by compression molding of the coverplate 3. However, the method for forming the thin portion in the coverplate is not limited thereto. For example, the thin portion may bemolded integrally with the cover plate using a press working capable offorming such a thin portion. Further, when the cover plate is producedby pressing, the pressing may be performed so that the thin portion isformed together.

Further, the above-mentioned embodiments describe a lithium ionsecondary battery cell. However, the type or the size (capacity) of thebattery cell is arbitrarily selected.

Further, the present invention is not limited to the lithium ionsecondary battery cell. The present invention can be applied also toprimary battery cells and capacitors such as electric double layercapacitors, in addition to various secondary battery cells.

The electric storage device (for example, a battery cell) may be usedfor an electric storage apparatus (a battery module in the case wherethe electric storage device is a battery cell) 50 as shown in FIG. 21.This electric storage apparatus 50 has at least two electric storagedevices and a bus bar member 51 that electrically connects the two(different) electric storage devices to each other. Further, theelectric storage apparatus includes a coupling member that couples theat least two electric storage devices to each other. In this electricstorage apparatus, the technique of the present invention needs to beapplied only to at least one of the electric storage devices.

REFERENCE SIGNS LIST

-   -   1 Case    -   2 Case Body    -   2 a Bottom    -   2 b Side Plate    -   2 c End Plate    -   2 d Opening    -   3 Cover Plate    -   31 Through Hole    -   32 Gas Discharge Valve    -   33 Injection Hole    -   34 Projecting Ridge (Projection)    -   35 Recess    -   36 Thin Portion    -   37 Case Inner Side Portion    -   4 Electrode Assembly    -   5 Positive Electrode Sheet    -   6 Negative Electrode Sheet    -   7 Separator    -   8 Current Collector    -   8 a Connecting Portion    -   9 Terminal Structure    -   10 Resin Plate    -   11 Outer Gasket    -   12 External Terminal    -   12 a Head    -   12 b Stem    -   13 Stopper    -   103 Cover Plate    -   134 Projection    -   203 Cover Plate    -   234 Projection    -   303 Cover Plate    -   334 Projection    -   403 Cover Plate    -   434 Projection    -   503 Cover Plate    -   534 Projection    -   603 Cover Plate    -   634 Projection    -   703 Cover Plate    -   734 Projection    -   803 Cover Plate    -   834 Projection    -   902 Case Body    -   902 b Side Plate    -   902 c End Plate    -   902 d Opening    -   902 e Corner Portion    -   903 Cover Plate    -   934 Projection    -   1003 Cover Plate    -   1034 Projection    -   1103 Cover Plate    -   1134 Projection    -   50 Electric Storage Apparatus    -   51 Bus Bar Member    -   A1 First Direction    -   A2 Second Direction    -   A3 Third Direction    -   P1 First Side    -   P2 Second Side    -   P3, P4 Side    -   S Trimming Step Portion    -   G Gap

What is claimed is:
 1. An electric storage device comprising: anelectrode assembly comprising a positive electrode plate and a negativeelectrode plate that are insulated from each other; and a case thathouses the electrode assembly, wherein the case comprises a case bodyhaving an opening, and a cover plate that is placed on an opening edgeof the opening of the case body so as to cover the opening, the casebody comprises a step portion at the opening edge, the cover platecomprises a projection that is inserted into the opening of the casebody, at least a portion of the projection opposes the step portionwithin the case body, and a seam between the cover plate and the openingedge of the case body is laser welded in at least the step portion. 2.The electric storage device according to claim 1, wherein the coverplate comprises a recess on an outer surface side of a portion where theprojection is provided.
 3. The electric storage device according toclaim 1, wherein the case body has a bottomed rectangular tubular shape,the step portion extends over at least one entire side of the openingedge of the case body, and the projection is formed at at least aposition corresponding to the one side.
 4. The electric storage deviceaccording to claim 3, wherein the case body has a bottomed quadrangulartubular shape, the step portion extends over each of a pair of opposedentire sides of the opening edge of the case body, and the projection isformed on the cover plate at at least positions corresponding to thepair of sides.
 5. The electric storage device according to claim 1,wherein the projection has an annular shape that extends along theopening edge of the case body.
 6. The electric storage device accordingto claim 1, wherein the projection is in contact with or adjacent to aninner surface of the opening edge of the case body.
 7. The electricstorage device according to claim 1, wherein the cover plate furthercomprises a case inner side portion that is inserted into the opening ofthe case body so as to be in contact with or adjacent to an innersurface of the opening edge, and the projection projects from the caseinner side portion.
 8. The electric storage device according to claim 1,wherein the projection is locally located in a vicinity of acircumference edge of the cover plate.
 9. The electric storage deviceaccording to claim 1, wherein the projection has an outercircumferential edge spaced at a distance from an inner surface of theopening edge.
 10. The electric storage device according to claim 1,wherein the projection has a linear shape that extends along the openingedge of the case body.
 11. The electric storage device according toclaim 1, wherein the projection has a tip in the projecting directionwith an arcuate cross section.
 12. An electric storage apparatuscomprising: at least two electric storage devices comprising at leastone electric storage device according to claim 1; and a coupling memberthat couples the at least two electric storage devices to each other.13. A method for producing an electric storage device, the devicecomprising: an electrode assembly comprising a positive electrode plateand a negative electrode plate that are insulated from each other; and acase that houses the electrode assembly and comprises a case body havingan opening, and a cover plate configured to cover the opening of thecase body, the method comprising: a step of irradiating a seam betweenthe cover plate and an opening edge of the case body with a laser, withthe cover plate being placed on the opening edge of the opening of thecase body, wherein the case body comprises a step portion at the openingedge, the cover plate comprises a projection that is inserted into theopening of the case body, at least a portion of the projection opposesthe step portion within the case body, and the seam is irradiated withthe laser at a position corresponding to the step portion in the laserirradiation step.
 14. The method for producing an electric storagedevice according to claim 13, wherein the projection is formed bycoining the cover plate from its outer surface toward its inner surface.15. The method for producing an electric storage device according toclaim 13, wherein a circumference edge portion of the cover plate, whichis placed on the opening edge of the case body, is subjected tocompression molding.
 16. The method for producing an electric storagedevice according to claim 13, wherein the projection is locally locatedin a vicinity of a circumference edge of the cover plate.
 17. The methodfor producing an electric storage device according to claim 13, whereinthe projection has an outer circumferential edge spaced at a distancefrom an inner surface of the opening edge.
 18. The method for producingan electric storage device according to claim 13, wherein the projectionhas a linear shape that extends along the opening edge of the case body.19. The method for producing an electric storage device according toclaim 13, wherein the projection has a tip in the projecting directionwith an arcuate cross section.
 20. The method for producing an electricstorage device according to claim 13, wherein the cover plate comprisesa case inner side portion that is inserted into the opening of the casebody, and a thin portion that is formed around a circumference edge ofthe cover plate and has a thickness smaller than the case inner sideportion, the projection projects from the case inner side portion, andH2≧H1+H3−H0 is satisfied, when a dimension in the thickness direction ofthe case inner side portion is H0, a dimension in the thicknessdirection of the thin portion is H1, a dimension in the thicknessdirection of the projection is H2, and a height difference in thethickness direction of the step portion is H3.
 21. A method forproducing a cover plate configured to cover an opening of a case bodythat houses an electrode assembly comprising a positive electrode plateand a negative electrode plate that are insulated from each other, themethod comprising: forming a projection that opposes, within the casebody, a step portion formed at an opening edge of the opening of thecase body, with the cover plate being placed on the opening edge, bycoining the cover plate at a corresponding position from its outersurface toward its inner surface.
 22. The method for producing a coverplate according to claim 21, wherein a circumference edge portion of thecover plate, which is placed on the opening edge of the case body, issubjected to compression molding.